1. Field
The following description relates to a reference voltage generating circuit and a light-emitting diode (LED) driver circuit having the same therein, and, for example, a reference voltage generating circuit which is capable of outputting a reference voltage, which corresponds to one of a plurality of LED strings having a lowest feedback voltage, at a timing when measuring the lowest feedback voltage of the corresponding LED string, and an LED driver circuit having the same.
2. Description of Related Art
A liquid crystal display (LCD) has a thinner thickness, a lighter weight, a lower driving voltage, and lower power consumption than other display types and, thus, has been widely used. However, the LCD is a non-emitting device that does not self-emit light and, thus, requires an additional backlight source to supply light to a liquid crystal panel.
A cold cathode fluorescent lamp (CCFL), a light-emitting diode (LED), or the like are often used as LCD panel backlight sources. Since the CCFL uses mercury, the CCFL causes environmental pollution, has a slow response speed, a low color reproduction, and is inappropriate to make a LCD panel light, thin, short, and small.
Since the LED does not use an environmental pollutant, the LED is environment-friendly and enables impulse driving. The LED also has a high color reproduction, is able to adjust light amounts of red, green, and blue LEDs to arbitrarily change a luminance, a color temperature, etc., and is appropriate to make a LCD panel light, thin, short, and small. Therefore, the LED has been often used as a backlight source of a LCD panel, etc.
If LED arrays, each of which includes a plurality of LEDs, are connected to one another in parallel in a LCD backlight unit (BLU) using LEDs, a driver circuit capable of supplying a constant current to each of the LED arrays is required. In addition, a dimming circuit is required to arbitrarily adjust a luminance, a color temperature, etc., or to compensate for a temperature.
For example, in order to maintain uniform brightness and color in backlight, all LEDs are driven by the same current regardless of feedback voltages Vf of the LEDs. For this control, a conventional technique uses a dynamic bus voltage regulation method to move a bus voltage VBUS according to deviations of LED arrays.
If the dynamic bus voltage regulation method is used, efficiency is improved. However, an output voltage fluctuates, and thus audible noise is generated.